This invention relates to a transmission lubrication system and more particularly to a transmission lubrication system particularly adapted for use with marine outboard drives.
In one form of marine outboard drive, the lower unit contains a bevel gear transmission which drives one or more propellers in selected directions. With this type of transmission there is frequently provided at the upper end of the unit a further transmission which may include the actual clutches and/or the reversing transmission for effecting the selected forward and reverse drives. Frequently, this type of arrangement employs a hydraulic pump that is driven off of the rear of the input shaft for this upper transmission and which draws lubricant from the lower unit transmission for actuating the clutches and/or lubricating components of the upper transmission.
Such a general environment may be best understood by reference to FIG. 1 of the drawings, which is a partially schematic cross-sectional view through an inboard/outboard drive that may be constructed either in accordance with the prior art or which may embody the present invention.
Referring specifically to this figure, an inboard/outboard drive which may be utilized with watercraft is identified generally by the reference numeral 11. This inboard/outboard drive includes an internal combustion engine 12 that is mounted forwardly of the transom of the associated propelled watercraft and within its hull. The engine 12 has an output shaft 13 that extends rearwardly through the transom and which is connected to a universal joint 14. The universal joint 14 transmits propulsion power to an input shaft 15 of a reversing transmission, indicated generally by the reference numeral 16, and which forms a portion of an outboard drive unit 17.
Although the invention is described in conjunction with an inboard/outboard drive, certain facets of the invention may be employed with outboard motors per se, as long as they incorporate a hydraulic pump disposed at the upper end of the outboard drive and a transmission at the lower end from which lubricant is drawn by the pump.
Continuing to describe this construction shown in FIG. 1, the input shaft 15 has journaled upon it a pair of bevel gears 18 and 19, which may be considered to be the forward drive and reverse drive gears, respectively. These gears 18 and 19 are constructed so as to be journaled on the input shaft 15 so that the input shaft 15 may rotate relative to the gears 18 and 19.
A hydraulically operated clutching mechanism, indicated generally by the reference numeral 21 and which may be of any known type utilized in this art, is provided in the reversing transmission 16. This hydraulically actuated clutching mechanism 21, which is actuated in a manner which will be described, selectively couples one of the gears 18 or 19 to the input shaft 15 so as to rotate with it.
The bevel gears 18 and 19 are enmeshed with opposite sides of a driven bevel gear 22. This driven bevel gear 22 is affixed for rotation with the upper end of a drive shaft 23 that is journaled within a drive shaft housing of the outboard drive 17. Because the gears 18 and 19 are enmeshed with diametrically opposite sides of the driven bevel gear 22, the direction of rotation of the driven bevel gear 22 and drive shaft 23 will depend upon which of the gears 18 or 19 is coupled for rotation with the input shaft 15.
As has been previously noted, the gear 18 is a forward drive gear, and when coupled to the shaft 15, the drive shaft 23 will be driven in a forward propulsion mode. In a like manner, when the reverse bevel gear 19 is coupled for rotation with the input shaft 15, the drive shaft 23 will be driven in a reverse drive mode.
In the illustrated embodiment, the propulsion unit 11 includes a pair of counter-rotating propellers comprised of a forward propeller 24 and a rearward propeller 25. The forward propeller 24 is coupled to a tubular shaft 26 that extends forwardly and is connected to a first bevel gear 27 of a final drive assembly, indicated generally by the reference numeral 28.
The rearward propeller 25 is coupled to an inner drive shaft 29 about which the tubular drive shaft 26 rotates. This drive shaft 29 is affixed to a second bevel gear 31. As a result of this arrangement, the propellers 24 and 25 will both be driven simultaneously when the drive shaft 23 is driven, but will rotate in opposite directions. The propellers 24 and 25 are of an opposite hand so that they will both provide a driving force when driven in either the forward or reverse directions.
As has been noted, the clutch actuating mechanism 21 is hydraulically operated. The hydraulic fluid for its operation is contained within the lower final drive 28 and is drawn upwardly to a hydraulic pump 32 which is driven off of the input shaft 15. A selector gear is provided for actuating either the clutch associated with the forward drive gear 18 or the clutch associated with the reverse drive gear 19, depending upon the operator's selection. The fluid in the clutch which is not energized is dumped back to the lower unit final drive 28.
The reversing transmission 16 and specifically the gears 18, 19 and 22 are also lubricated by means including the pump 32. Thus some of the pump output is delivered to these gears.
The disadvantages of the prior art type of construction may be best understood by reference to FIG. 2, which is a large schematic view, in part similar to FIG. 1, but shows in more detail how the fluid is circulated.
The same reference numerals are applied to FIG. 2 as are utilized in FIG. 1 to identify the various components. In this figure, however, only a single propeller drive illustrated because this is the more conventional type of arrangement, and the final drive for driving the propeller shaft 31 is identified by the reference numeral 51. The transmission is still indicated by the reference numeral 28. It will be seen that a supply conduit 52 extends through the outboard drive unit 17 from an area at the upper end of the transmission casing 28 and connects to the fluid pump 23. This supply conduit has an inlet opening 53 disposed at the upper end of the case.
In addition to supplying lubricant for actuating the clutches 21 and as has been noted, the pump 32 also supplies lubricant that lubricates the gears within the reversing transmission 16. These gears are, therefore, contained within their own housing. A return conduit 54 extends from this housing back to the final drive housing 28 and discharges into the gear case containing the final drive transmission 28.
As indicated in FIG. 2, any air present in the prior art type of construction will tend to be drawn through the inlet opening 53 and delivered to the pump 32 through the conduit 52. To minimize the amount of air so drawn, it is the practice to totally submerge the lower unit, final drive transmission 28 in lubricant. In other words, the lubricant fills the total lower unit. This has a distinct advantage in that it means that the gears therein are totally immersed in lubricant, even though this much lubricant is not required for their lubrication. Therefore, there will be a large drag on the gears.
In addition, there is always the danger that as the lubricant level falls, no lubricant will be supplied to the reversing transmission 16 or available for actuation of the clutches 21.
It is, therefore, a principal object of this invention to provide an outboard drive transmission of this general type, but wherein these disadvantages are avoided.
It is a further object of this invention to provide an improved transmission lubrication system for a marine outboard drive wherein adequate lubrication is provided, but wherein drag on the gears lubricated can be reduced by avoiding submerging them completely in lubricant at least when the unit is being driven.
It is a further object of this invention to provide an improved hydraulic clutch actuating mechanism associated with a transmission wherein the clutch can be supplied with sufficient fluid for actuation, but wherein the transmission drag losses are substantially reduced.